The basic aim of this project remains as it was: to study the neurophysiological effects of psychotogenic drugs upon brain neurons whose presumed transmitter substance bears a chemical relationship to the drug in question. There are two major types of psychotogenics under study: 1. The indoleamine type drugs (e.g. D-lysergic acid diethylamide, and N, N- dimethyltryptamine); effects of these drugs are being studied on serotonin-containing neurons in brain, and: 2. The amphetamines: effects on catecholamine-containing neurons in brain are being investigated. The principal neurophysiological effects under study are alterations in single unit activity that may result from the systemic or microiontophoretic (direct) administration of drugs or putative transmitter substances. Neurons are selected for study either because they contain a drug-related endogenous substance or because they receive input from such neurons. The experiments are being conducted upon the mammalian (rat) brain, and histochemical methods are utilized for the identification, on a cellular level, of the pre- or postsynaptic elements within the neurochemical systems under investigation. Brains obtained from animals in which unit recordings are performed are invariably subjected to standard histological or fluorescence histochemical analysis in order to correlate electrophysiological responses with neurochemical identity. Results to date show that the psychotogenic drugs have marked effects on the physiological activity of both pre- and postsynaptic neurons within brain monoamine systems. BIBLIOGRAPHIC REFERENCES: Aghajanian, G.K., and Gallager, D.W. Raphe origin of serotonergic nerves terminating in the cerebral ventricles. Brain Res., 88: 221-231, 1975. Davis, M., Svensson, T. H., and Aghajanian, G.K. Effects of de- and l- amphetamine on habituation and sensitization of the acoustic startle response in rats. Psychopharmacologia, 43: 1-11, 1975.